A traditional solution in the purpose described above and particularly in square shaped basins is such, that the fluid processing apparatus, such as a clarification basin or like, comprises usually a special kind of a scraper bar arrangement, which has several scraper bars, existing one after the other in the longitudinal direction of the basin, and movement means for moving the same, such as two chains, being placed parallelly and being driven by means of a drive wheel and idle wheel assembly, in connection with which the scraper bars are fastened removeably particularly in order to make easier the service and maintenance of the scraper bar arrangement. The type of scraper bar arrangements mentioned above are nowadays being used e.g. in connection with clarification basins in a way that the scraper bar/bars is/are transferred by chains, moving at opposite side or intermediate walls of the basin, alternatively on the surface and at the bottom of the basin, scraping sludge existing at the bottom to a sludge pocket while passing along the bottom, and, respectively guiding material existing on the surface to a collecting chute, which goes crosswise through the basin, while passing on the surface. There are also scraper bar arrangements, in which the bars are being moved e.g. by means of a carriage, moving above the basin, or e.g. by hydraulic arrangements. Also the shape of the basin may be in practice almost of whatever form.
In this connection, the surface scum is traditionally exhausted in a so to speak indirect manner, whereby the scrapers while passing on the surface, guide the material on the surface towards the collecting chute in a so called free-drifting manner. The collecting chutes, being used in this connection, are usually mechanically operated “suction chutes”, which are being rotated from time to time around a longitudinal axis to a position, in which the surface scum is being “gulped” inside the same in order to lead it subsequently away from the liquid basin. On the other hand, in this connection a suction chute is used also, which has a moveable front wall, the operating principle of which is, however, in practice the same as described above.
A problem related to this kind of suction chutes is the fact that they take along too much surface water, which can thus drift along with the surface scum furthermore to the exhaustion channel of the surface scum. Also the bearing of such rotating suction structures to the walls of the basin is very difficult to carry out structurally, which is why among other things leaks are caused. In addition to the above, the suction chutes easily tend to get jammed among other things due to temperature differencies. The type of mechanically operated chute arrangements described above require naturally also operating devices and automation in order to move the chutes, which is why this kind of implementations require a very dense service and maintenance in order to keep them operable. Furthermore, a problem in practice related to this kind of solutions is due to exessive surface scum that gets collected on the surface of the liquid basin, together with which also other impurities may get collected. It is thus very usual that also organic processes may take place in the surface scum among other things in the form of algal growth.